The US stock market is shrinking, and investors are pulling their money out at a near-record pace as storm clouds gather over the US economy.

That means the titans of Wall Street may have to contend with choppy water as they cruise toward their Nantucket getaways this year.

What's happening: "Sell in May and go away" is a popular Wall Street-ism that describes the trend of investors closing up shop and sorting out their portfolios ahead of vacations. It also alludes to the historical underperformance of stocks during the summer months.

But recent trading flows show that something larger is at play this year.

Bank of America analysts said on Tuesday that their clients have now been large net sellers of US stocks for five weeks in a row. Just last week, they sold off $5.7 billion more in stocks than they purchased, the highest outflow since last July.

Bank of America recorded the second largest sell-off of tech stocks in their history last week. And while one week does not a trend make, it does stand in stark contrast with the Magnificent Seven fervor that ensnared Wall Street mere months ago.

Low volumes, eventful markets: The tides appear to have shifted and the usual summer doldrums are nowhere to be found.

"Summer 2024 may prove volatile, with momentum stalling amid policy uncertainty," wrote Morgan Stanley Wealth Management Chief Investment Officer Lisa Shatlett in a note this week.

"Economic crosscurrents have left the [Federal Reserve] more tentative regarding rate cuts, amplifying the potential significance of each data point as debate continues over the degree of policy restriction," she said.

A series of weak Treasury auctions could also roil markets, not to mention the ongoing and closely contested upcoming presidential election. Market volatility in an election year tends to pick up in October, but low trading volume and large potential catalysts could mean big swings in the weeks to come.